SILVER
PERCH - Bidyanus
bidyanus
Rob McCormack
The Silver Perch is a native Australian species.
Basically a native of the Murray Darling
drainage system, this species over the years has
been widely distributed across NSW and many
eastern flowing streams now have small
populations. Silver perch are omnivores
with a very varied diet consisting of small food
items such as insects, insect larvae, shrimps,
yabbies, molluscs, worms, weeds and algae.
They do not grow to extreme size and specimens
over 3Kgs are rare. Rumour has it they
grow to 8Kgs but I have seen them up to 4Kg
only. Generally in farm dam situations
they will grow to approximately 2Kgs.
Silver Perch are one of the main Aquaculture
species in NSW, the reasons for this are
numerous, but some of them are given by Stuart
Rowland from NSW Fisheries as:
1. Established
hatchery techniques
2. A
hardy fish that can be held
in captivity at high
densities.
3. Rapid
and uniform growth.
4. Omnivorous.
5. Amenable
to artificial feeding.
6. Non
– cannibalistic.
7. Diseases
under hatchery conditions
known.
8. High
meat recovery of 40%.
9. Marketing
attributes, including an
Australian native fish.
10. Attractive
appearance and colour.
11. Excellent
cooking and eating
qualities.
12. White
flesh, few bones.
Silver Perch also have a few disadvantages,
these include:
1. The
readily take up off flavour
compounds from growout
ponds.
2. This
requires post harvest
purging to remove off
flavours.(Earthy taste)
3. Purging
takes 1 – 3 weeks and
increases production costs.
4. This
requires gentle capture and
handling to ensure survival
in purging tanks.
5. Silver
Perch are not as robust as
some species and are very
sensitive to mishandling.
6. Silver
Perch have been sold in the
past unpurged, referred to
as road kill these fish have
damaged the market potential
of good quality purged fish.
7. Fish
build up large fat contents
in gut cavity.
8. Feed
costs are high and
growing.
Silver Perch are not only grown commercially but
are widely stocked into farm dams as a
recreational species. There are two main
reasons for this, firstly Silvers are very fast
growing and most people can start catching and
eating silvers 12 - 18 months after initial
stocking. They are also excellent sporting
fish on light line and accept worms or peeled
prawns readily. They do not however
actively attack lure like bass, we occasionally
catch silvers on lures but they are generally
chasers not biters. They also eat bread
and many people feed their fish bread in the
pond. This burlies the fish up to the
surface and creates considerable satisfaction
for the farmer who can now see how well the fish
are growing and show them of to his family and
friends, after bringing them to the surface with
bread, a quick catch can always be made by
adding a bit of bread to a hook.
Silvers do not breed in a pond, they are
basically a river fish and need flowing water.
This means you only get out as many fish as you
put in so most people would add extra stock each
year. As silvers are not cannibalistic and
have a small mouth adding little fellers in with
the big guys is not a problem as it is with
other species.
Silver perch are a river species that generally
spawn in summer during flood condition. In
the wild these fish school together and have a
migratory run upriver to spawn. They
travel considerable distances even hundreds of
kilometres upstream and like to spawn when the
river is in flood with water over the flood
plain. The eggs once released roll in the
current across the bottom down river and hatch
24 hours later. By spawning in flood the
predators for the eggs are few and far between
and survival is high. Unfortunately the
construction of weirs and dams has severely
restricted the movement of spawning Silvers
upstream and reduced flood events. Silver
perch eggs also don’t like salty water so the
increase in salinity levels in many inland
streams is detrimental. All this has led
to a reduction of silvers in the wild and they
are on the Potentially Threatened List.
In the early 60”s NSW DPI Fisheries started
breeding research at Narrandera and ever since
then NSW DPI Fisheries have considered Silver
Perch as a ideal species for aquaculture in NSW.
NSW DPI Fisheries has devoted considerable
resources to Silver Perch culture over the years
and thanks to those efforts we now have a 300
tonne per year aquaculture industry in NSW.
This may be small by international standards but
for the small family farmers in NSW utilising
their own capital it is a very satisfactory
effort.
Breeding Silver Perch –
Unfortunately silver perch do not breed
naturally in farm dams. This means you
only get out what you put in. Silver perch
breeding is a specialised business that is
conducted by commercial fish hatcheries.
These hatcheries artificially breed silvers and
then supply the fingerlings (small fish) to
other commercial farmers for ongrowing or direct
to the public to stock their dams.
Breeding silvers requires capture of adult
sexually mature fish from ponds. Though
the fish do not naturally breed they do roe up
ready to go. Breeding season starts mid
September and runs through to April depending on
where in NSW you are located. Fish
captured are anaesthetised with clove oil
weighed and injected with HCG (human chorionic
gonadotropin) at a rate of 200IU/Kg. The
hormone is just that little push the fish need
to get them to breed. Females are always
injected but males are usually ready to go most
times and don’t need any drugs to help them
along. Most breeders use a ratio of 2
males to 1 female, generally one of those males
is injected and one is not. Silvers are a
school fish so in a 1500 litre tank you could
use 3 females on 6 males. This gives us a
good genetic mix in any given batch of fish.
36 hours after injection the fish spawn
naturally in the tank. This is the beauty
of hormones it makes all the fish breed at the
same time. We try to inject fish at 6pm in
the afternoon so they will breed 36 hours later
at 6 am. We usually leave the fish an hour
for the eggs to water harden then use a scoop
net to remove the fish. The eggs are kept
in the dark at 24 Deg C and with high aeration
to keep the eggs in suspension. Fertility
rates of the eggs vary between batches but
anything over 80% is good. Silver perch
have approximately 125,000 eggs per Kg of fish
so quite a few in the tank. The eggs hatch
24 hours after spawning and we start putting
them out into the ponds 4 – 7 days after they
hatch. We prepare the outside fingerling
ponds by adding lime and fertilizer then
flooding with water. It is critical that
ponds are dry and cracked between batches of
fish to ensure that no contamination occurs.
Depending on the weather and the long range
forecast we may fill the ponds with water up to
a week before we inject the fish. Other
times we fill the pond on the same day we inject
the fish. It’s a real balancing act, we
are trying to grow zooplankton in the ponds to
feed the larvae when released. If we fill
the pond too late the food does not have enough
time to grow and the fish starve. If we
fill it too soon the zooplankton is too big and
eats the fish larvae and we end up with nothing.
Air and water temperatures are the key as
everything grows faster in warm water then cold.
Once in the pond is when the real fun begins as
Silvers when small are vulnerable to all types
of problems from water quality to disease or
parasites. We regularly check the water
and the fish to attempt to solve minor problems
before they become major ones.
For the first two weeks after fish are released
into the pond no feeding is required as they
live of the zooplankton in the pond. After
2 weeks we start adding artificial food.
This is fingerling dust, a fine powder which is
thrown by hand into the pond twice daily.
The small silvers eat both the dust and
zooplankton initially but as they grow and their
hunger increases the zooplankton can not
reproduce fast enough and numbers drop.
Silvers grow fast and 6 – 8 weeks after release
they are ready for harvest. Fingerlings
are captured from the ponds and then held in
holding tanks where they have a salt bath and
are checked for any disease, parasites of
deformities. If everything is OK they are
ready for sale to other commercial silver perch
farms or direct to the public for aquarium pets,
aquaponic stock, fish ponds or farm dams. etc.
If you would like to buy Silver Perch
fingerlings then try one of these fish
hatcheries:
- 12 Mile Aquaculture Farm (12 Mile Crk
NSW) Nigel Stoeckel
